1. Field of the Invention
This invention relates to a process for making salts and fatty acid esters of isethionic acid, which minimizes the formation of unwanted by-products. It also relates to the ester compositions produced.
2. Description of the Related Art
Sodium, other alkali metal, and ammonium salts of the fatty acid esters of isethionic acid (2-hydroxyethanesulfonic acid) are useful as mild, foaming surfactants. These isethionate ester salts are usually manufactured by first forming an isethionate salt by reaction of ethylene oxide with an aqueous solution of a bisulfite salt such as sodium bisulfite or ammonium bisulfite. The free alcohol functionality of the isethionate salt is then esterified with a fatty acid to produce a fatty acid ester of the isethionate salt.
One of the principal problems encountered in this process is the production of ethylene glycol as a by-product during the reaction of ethylene oxide and the bisulfite salt. The ethylene glycol thus formed subsequently reacts with the fatty acid in the second step of the process, resulting in the formation of mono- and di-esters of ethylene glycol which are only partially soluble in aqueous-based formulations of the acyl-isethionate products wherein the solids content is greater than 30% by weight. These partially soluble materials result in the formation of a hazy, aqueous product that contains fine solids which are difficult and costly to remove.
It would be advantageous to avoid the formation of the ethylene glycol fatty acid esters so that a clear aqueous product could be obtained without the need for additional processing steps which add to the cost of the product. The present invention is a method for making fatty acid esters of alkali metal and ammonium isethionates which minimizes the formation of ethylene glycol, which in turn lowers the chance that fatty acid esters of ethylene glycol will form and contaminate the final product.